For most people who develop Parkinson's there is no clear underlying cause. However, the investigators are particularly interested in the minority of people diagnosed with Parkinson's who have either early onset disease and/or other relatives affected with Parkinson's. The investigators believe that variations in inherited material (genes) can sometimes cause the disease, and this may run in families. This opens the door to a range of studies on the effects of gene variation at a nerve cell and brain level, which the investigators hope will lead to new targeted treatments.